January | 2016 | chugchug

The idea is to get lower gear ratio for my road bike to help climbing steep hills.

Rational

I like climbing hills on my bike. Particularly going up to Skyline BLVD and down towards the ocean. My problem is that I find myself using the 1st gear all the time and even then I often can’t maintain a fast enough cadence. The gear ration of the Shimano 105 components on my road bike is already the lowest possible. My only option is to use mountain bike (MTB) components. This article is about changing the rear cassette.

Cassette

Change from Shimano 105 11-speed 11-32T – CS-5800 to XT CS-M8000 11-speed 11-40T – XT CS-M8000 will add 2 more gear options at the low end. The numerical ratio will be 25% lower, or from gear inch 28 to 22.5.

The 11-42T version of this cassette only works with a single chainring setup. There are 30T, 32T and 34T options. It is actually quite compelling. My bike has a 34-50T compact crank and 11-32 cassette to create a gear inch range of 28-120. A single 34T chainring with 11-42T cassette has a gear inch 21.5-80.

Cassette Compatibility: Shimano 11 speed hub on road bikes is 1.85mm longer than the 11 speed MTB (11 speed MTB hub is the same as the 10 and 9 speed hubs). They make a spacer called “low spacer” for this – 1.85mm Low Spacer

Chain

CN-HG700 seems to be compatible for both road and MTB 11-speed systems. My bike uses 56 inch chain (112 links) the new chain comes with 114 links or 57 inch. Calculating the required chain for the new bike (40T Cassette, 50T Chainring, 42.5CM chainstay) I need 58 inch. I will need to purchase 2 chains and combine them to make the length I need. – Calculator . Going with a 1-11 solution with a 34T chainring and 11-42T cassette the chain needs to be 54 inch.

Derailleur/Shifter

Shimano design derailleur and shifters for 11-speed bikes as sets. They are expected to work together, and with the specific cassette design. The combination currently installed on my road bike will not work with a MTB cassette for several reasons.

Cog Clearance

The road derailleur currently on the bike – RD-5800 will not clear the large cogs on the 11-40T cassette. Wolf Tooth Components makes an adapter RoadLink that may be able to solve this problem. Alternatively, a MTB derailleur RD-M8000 might be a better solution.

Cog Pitch, Derailleur Shift ratio, Shifter Cable Pull

MTB cassette cog pitch is 3.9mm and road cassette is 2.7 Compatibility. With the road derailleur/shifter combination, it may be possible to tweak the attachment point of the cable. This will cause the derailleur to move the required distance to the next cog. If switching the the MTB derailleur there are 2 possibilities: 1) use MTB shifter, which adds a new problem of how to attach it; 2) use Shiftmate 8 from Jtek with the current road shifter.

The Shiftmate adapter uses a wheel with 2 grooves with different diameter. The cable enter the wheel around one groove and exit around the other which changes the amount of pull the derailleur see.

MTB Shifters on Road Bike

There are some articles describing how to modify a front derailleur braze-on 31.8 mm strap to so it can accept a MTB shifter and attach it to the thick part of a road dropped handlebar. This makes it possible to shift but not from the STI shifter. switching between sscx mode and touring and Paul Components.